Some of his TV credits include roles in BlackJack: Sweet Science, Love Bytes and White Collar Blue.

"[14] He left The Shield in 2007 after he won the lead role on the CBS series Moonlight, where he played private investigator and vampire Mick St.

There was speculation that the series would be dropped but fan pressure prevailed and the show was given four additional episodes to try to regain its audience share.

After its cancellation, a fan-based charity campaign to win a second-season renewal for Moonlight by holding blood drives proved unsuccessful.

[17] He was cast in the lead role of the CBS hospital drama Three Rivers, developed by producer Carol Barbee, which aired Sunday evenings in the 2009–2010 season.

[20] O'Loughlin was cast in the CBS remake of Hawaii Five-0 portraying Lieutenant Commander Steve McGarrett,[21] which premiered on 20 September 2010.

[23] On 2 March 2012, CBS announced that O'Loughlin would miss shooting some episodes of Hawaii Five-0 to seek drug treatment related to pain management medication prescribed after a shoulder injury.

[33] O'Loughlin is an experienced practitioner of Brazilian Jiu-Jitsu, training alongside his Hawaii Five-0 co-star Scott Caan and MMA veteran Egan Inoue.

At the 2022 ADCC World Championship, O'Loughlin was promoted to black belt in the martial art in front of the crowd in attendance.